•A framework integrating the moment-rotation approach into a nonlinear analysis of concrete beams is introduced.•The proposed partial interaction model accounts for the effect of cracking on beam behavior, capturing lost stiffness due to crack formation.•The model accurately simulates the load–deflection, crack opening-moment and moment–curvature for concrete beams with and without fibers.•Partial interaction approach exhibits greater accuracy in predicting the behavior of beams under ultimate loads.•The study evaluates the impact of GFRP reinforcement stiffness loss on the global responses of structural elements. The moment-rotation approach is a promising methodology aimed to predict the rotational capacity of reinforced concrete members. Recently, several authors have applied this method to evaluate the bending behavior of beams, replacing the moment–curvature approach. Considering the partial interaction phenomena, the moment-rotation approach can be used to develop parametric analyses and to assist in the formulation of rational equations for different material combinations. However, the techniques to integrate the moment-rotation approach into a nonlinear structural analysis have not been deeply explored, and the wider use of this methodology requires a rigorous validation. This study proposes and validates a modeling framework that integrates the moment-rotation approach into a reinforced concrete beam analysis based on the conjugate beam method. This model simulates the global stiffness decrease of beams as the cracking progresses. The numerical results were compared with experimental tests from literature performed on fiber-reinforced and plain concrete beams with glass‐fiber reinforced polymer (GFRP) bars. The experimental behavior of deflection, the crack-opening moment, and the moment–curvature were accurately simulated, especially for fiber-reinforced concrete beams. This accuracy indicates that the strategy adopted to integrate the moment-rotation approach into a structural analysis is definitely promising when modeling beams made of new materials.